Variable valve operating system of internal combustion engine enabling variation of valve-lift characteristic

Abstract

In an engine employing a variable lift and working angle control mechanism enabling both a valve lift and a working angle of an intake valve to be continuously simultaneously varied depending on engine operating conditions, the control mechanism includes at least a rocker arm and a control shaft formed integral with an eccentric cam. The valve lift characteristic of the control mechanism varies by changing an angular position of the control shaft. A control-shaft position sensor has a directivity for the sensor output error occurring owing to a change in relative position between the control shaft center and the position sensor. The error becomes a minimum value in a specified direction of relative position change. The specified direction of relative position change is set to be substantially identical to a direction of a line of action of load acting on the center of the control shaft during idling.

What is claimed is:  
     
       1. A variable valve operating system of an internal combustion engine comprising: 
       a drive shaft adapted to be rotatably supported on an engine body and to rotate about an axis in synchronism with rotation of a crankshaft of the engine;  
       a control shaft adapted to be rotatably supported on the engine body;  
       an actuator driving the control shaft to adjust an angular position of the control shaft;  
       an intermediate member that rotary motion of the drive shaft is converted into either of rotary motion and oscillating motion of the intermediate member, a center of the motion of the intermediate member with respect to the engine body varying depending on the angular position of the control shaft;  
       the intermediate member linked to an intake valve of the engine, for lifting the intake valve responsively to the motion of the intermediate member, a valve lift characteristic of the intake valve being varied depending on a change in the center of the motion of the intermediate member;  
       a position sensor attached to the engine body to generate a sensor signal indicative of the angular position of the control shaft;  
       the position sensor having a directivity for an error contained in the sensor signal owing to a change in relative position between a center of the control shaft and the position sensor, the error becoming a minimum value in a specified direction of the relative position change; and  
       the specified direction of the relative position change being set to be substantially identical to a direction of a line of action of load acting on the center of the control shaft during idling.  
     
     
       2. The variable valve operating system as claimed in  claim 1 , wherein: 
       under a valve lift characteristic used during idling, the specified direction of the relative position change is included in a predetermined area defined between a direction of load acting on the center of the control shaft at an intake valve open timing and a direction of load acting on the center of the control shaft at an intake valve closure timing.  
     
     
       3. The variable valve operating system as claimed in  claim 1 , wherein: 
       under a valve lift characteristic used during idling, the specified direction of the relative position change is substantially identical to a direction of load acting on the center of the control shaft at a maximum valve lift point.  
     
     
       4. The variable valve operating system as claimed in  claim 1 , which further comprises: 
       a pin-slit coupling mechanism through which the position sensor and the control shaft are coupled to each other, the pin-slit coupling mechanism comprising:  
       (i) a pin attached to a shaft end of the control shaft so that an axis of the pin is eccentric to an axis of the control shaft; and  
       (ii) a portion defining therein armadillo-elongated slit in engagement with the pin, the portion defining the slit being fixedly connected to the position sensor; and wherein:  
       a direction of a centerline of the slit is set to be substantially identical to the specified direction of the relative position change, the specified direction of the relative position change varying depending on the angular position of the control shaft.  
     
     
       5. The variable valve operating system as claimed in  claim 4 , wherein: 
       the position sensor comprises a rotary potentiometer.  
     
     
       6. The variable valve operating system as claimed in  claim 1 , wherein: 
       the position sensor comprises a non-contact sensor having an electromagnetic pickup fixedly connected to the engine body and a toothed disc attached to a shaft end of the control shaft; and  
       a direction of a line segment interconnecting the center of the control shaft and the electromagnetic pickup is set to be identical to the specified direction of the relative position change.  
     
     
       7. The variable valve operating system as claimed in  claim 1 , wherein: 
       the control shaft formed integral with an eccentric cam;  
       the intermediate member comprises a rocker arm supported on an outer periphery of the eccentric cam to permit the oscillating motion of the rocker arm; and  
       the drive shaft having a rockable cam rotatably fitted on an outer periphery of the drive shaft, so that the motion of the rocker arm is transmitted via the rockable cam to the intake valve.  
     
     
       8. A variable valve operating system of an internal combustion engine comprising: 
       a drive shaft adapted to be rotatably supported on an engine body and to rotate about an axis in synchronism with rotation of a crankshaft of the engine, the drive shaft having a first eccentric cam fixedly connected to an outer periphery of the drive shaft;  
       a link arm rotatably fitted onto an outer periphery of the first eccentric cam;  
       a control shaft adapted to be rotatably supported on the engine body, the control shaft formed integral with a second eccentric cam;  
       an actuator driving the control shaft to adjust an angular position of the control shaft;  
       a rocker arm rotatably supported on an outer periphery of the second eccentric cam so that the oscillating motion of the rocker arm is created by the link arm;  
       a rockable cam rotatably fitted on the outer periphery of the drive shaft;  
       a link member mechanically linking the rocker arm to the rockable cam so that the oscillating motion of the rocker arm is converted into an oscillating motion of the rockable cam and that the intake valve is pushed by the oscillating motion of the rockable cam;  
       a valve lift and a working angle of the intake valve simultaneously varying by changing an angular position of the second eccentric cam of the control shaft;  
       a position sensor attached to the engine body to generate a sensor signal indicative of the angular position of the control shaft;  
       the position sensor having a directivity for an error contained in the sensor signal owing to a change in relative position between a center of the control shaft and the position sensor, the error becoming a minimum value in a specified direction of the relative position change; and  
       the specified direction of the relative position change being set to be substantially identical to a direction of a line segment interconnecting a center of the drive shaft and the center of the control shaft, during idling.  
     
     
       9. An internal combustion engine comprising: 
       a variable lift and working angle control mechanism that enables both a valve lift and a working angle of an intake valve to be continuously simultaneously varied depending on engine operating conditions; the variable lift and working angle control mechanism comprising:  
       (a) a drive shaft adapted to be rotatably supported on an engine body and to rotate about an axis in synchronism with rotation of a crankshaft of the engine;  
       (b) a control shaft adapted to be rotatably supported on the engine body;  
       (c) an actuator driving the control shaft to adjust an angular position of the control shaft; and  
       (d) an intermediate member through which rotary motion of the drive shaft is converted into either of rotary motion and oscillating motion of the intermediate member, a center of the motion of the intermediate member with respect to the engine body varying depending on the angular position of the control shaft, the intermediate member linked to the intake valve, for lifting the intake valve responsively to the motion of the intermediate member, and a valve lift characteristic including both the valve lift and the working angle of the intake valve being varied depending on a change in the center of the motion of the intermediate member;  
       sensor means attached to the engine body for generating a sensor signal indicative of the angular position of the control shaft, the sensor means having a directivity for an error contained in the sensor signal owing to a change in relative position between a center of the control shaft and the sensor means, the error becoming a minimum value in a specified direction of the relative position change; and  
       the specified direction of the relative position change being set to be substantially identical to a direction of a line of action of load acting on the center of the control shaft during idling.  
     
     
       10. The variable valve operating system as claimed in  claim 9 , wherein: 
       the sensor means comprises a rotary potentiometer.  
     
     
       11. The variable valve operating system as claimed in  claim 9 , wherein: 
       the sensor means comprises a non-contact sensor having an electromagnetic pickup fixedly connected to the engine body and a toothed disc attached to a shaft end of the control shaft; and  
       a direction of a line segment interconnecting the center of the control shaft and the electromagnetic pickup is set to be identical to the specified direction of the relative position change.